HealthDay News -- Older adults who down several diet drinks a day may have a heightened risk of developing depression, a new study suggests.

Researchers found that of more than 260,000 older adults in a U.S. survey, those who had at least four daily servings of artificially sweetened soda, iced tea or fruit punch were at increased risk of being diagnosed with depression in the next decade.

People with a taste for sugar-sweetened drinks also showed a higher depression risk versus those who avoided the beverages. But the link was weaker than the one between diet drinks and depression, according to the study, which was released Jan. 8.

On the other hand, coffee lovers had a slightly lower depression risk than people who typically passed on the java.

What it all means, however, is anyone's guess.

"This probably creates more questions than it answers," said Eva Redei, a professor of psychiatry at the Northwestern University Feinberg School of Medicine in Chicago. And it definitely is not possible to lay the blame on diet drinks themselves, based on these findings alone, said Redei, who was not involved in the study.

Caution is in order, agreed study leader Dr. Honglei Chen, an investigator at the U.S. National Institute of Environmental Health Sciences.

"The research is preliminary and more investigation into the topic is needed," Chen said.

But, he added, the findings are "intriguing," and are consistent with a small but growing number of studies linking artificially sweetened drinks to poorer health.

The results were released by the American Academy of Neurology, ahead of its annual meeting in San Diego in March.

The findings are based on more than 260,000 Americans aged 50 to 71 who reported on their usual beverage habits. About a decade later, they were asked whether they'd been diagnosed with depression in the past several years.

Slightly more than 4 percent said they had. In general, people who consumed the most aspartame-sweetened diet beverages at the outset had a higher depression risk. Those who had downed at least four cans or cups of diet soda a day were 31 percent more likely to report depression than nondrinkers.

High intakes of artificially sweetened fruit punch and iced tea were linked to similar risks. Regular soda was as well, but the increased risk -- at 22 percent -- was lower than that linked to diet soda.

In contrast, people who had four or more cups of coffee a day had a roughly 10 percent lower risk of depression versus nondrinkers.

"This is an interesting study, and it's based on a large population," Redei said. She added that it's unusual for depression studies to focus on older adults, so it is good to see researchers look into the risk factors for later-life depression.

The problem is that many other factors might explain why diet drinks or coffee have a relationship with depression risk.

Two big ones are diabetes and obesity, Redei said. Both are common among older Americans, and both conditions are linked to higher odds of developing depression. People who are obese or have diabetes may favor diet drinks to help control their weight or blood sugar.

As for coffee, it may just be that healthy adults feel more free to drink a lot of it. "Older adults in poorer health may have been advised by their doctors to avoid caffeine," Redei said. And poorer physical health may translate into a higher depression risk.

Chen said his team statistically adjusted for many other factors, including weight and any reports of diabetes.

He noted, though, that overall lifestyle or other factors could still account for the findings. And it's not clear, Chen said, why diet drinks or coffee would have some direct effect on depression risk.

Until more is known, Redei cautioned older adults against lining up at Starbucks to help cut their depression risk.

Studies presented at medical meetings are generally considered preliminary until they are published in a peer-reviewed journal.